No, the coins i have are no pennies. They are shiny silver coins. There is no value printed on them, but if i remember correctly the shopkeeper said they were 25 pence pieces.
Ok, searched on Google for 25 pence and found a picture of the coin:
http://acneskinclinic.com/ebay0806/06082100.jpg
The picture is a bit dark, but the coin actually looks very nice, better than the dollar coins. I compared this coin to the dollars i have and they are not only a bit thicker, but also a tiny bit bigger than the dollar coins. A stack of 3 English coins are as big as a stack of 4 dollars.
The edges of the dollar coins are rougher than the 25 pence coins, so the dollars are a bit better for palming.
Anyway, for a trick that needs nice big coins i would recommend the 25 pence coins. Since they were not that expensive i think there are a lot more of them around, so they should be easy to find in coin collector shops.